Method of deep well cementing

ABSTRACT

A method utilizing a sequential injection of ever-decreasing weight drilling muds into wells for the total displacement of high density drilling mud from the wellbore. Wellbore cementing is accomplished through the introduction of a wellbore cement having substantially the same weight as the drilling mud remaining within the wellbore after displacement of the high density drilling mud. The cement introduced easily displaces the drilling mud present in the well so that adequate contacting of the casing, cement and wellbore walls is achieved with no residual high density drilling mud remaining within the casing completion.

United States Patent 1191 Byrd METHOD OF DEEP WELL CEMENTING [75]inventor: Ottis G. Byrd, Jackson, Miss.

[73] Assignee: Cities Service Oil Company, Tulsa,

Okla.

[22] Filed: April 7, 1971 [21] Appl. No.: 131,962

[52] U.S. Cl ..166/312 [51] Int. Cl. ..E2lb 37/00 [58] Field ofSearch..... ..l66/312, 311, 291, 285; 175/65, 70

[56] References Cited UNITED STATES PATENTS 11/1968 McKinney ..l66/312X2/1962 Caldwell ..l66/312X 1March 13, 1973 2,836,246 5/1958 l-loch..166/3l2 X Primary Examiner-Robert L. Wolfe Attorney-J. Richard Geaman[57] ABSTRACT A method utilizing a sequential injection ofeverdecreasing weight drilling muds into wells for the totaldisplacement of high density drilling mud from the wellbore. Wellborecementing is accomplished through the introduction of a wellbore cementhaving substantially the same weight as the drilling mud remainingwithin the wellbore after displacement of the high density drilling mud.The cement introduced easily displaces the drilling mud present in thewell so that adequate contacting of the casing, cement and wellborewalls is achieved with no residual high density drilling mud remainingwithin the casing completion.

7 Claims, 1 Drawing Figure PATENTEUuAmma 3,720,266

OTTIS G. BYRD INVENTOR,

' yWMm ATTORNEY.

METHOD OF DEEP WELL CEMENTING BACKGROUND OF THE INVENTION bow with thefirst portion of the ever-decreasing The present invention relates to amethod of deep exceptionally high weight are utilized in order tocontrol high pressure gas deposits contained within the formationsencountered by the drilling bit. The problem develops when cement isintroduced or squeezed into these wells in an attempt to displace thehigh density drilling mud contained therein. Normally, the cement tendsto channel or viscous fingering occurs with the cement channelingthrough the high density drilling mud contained within the wellbore suchthat inadequate contacting of cement with wellbore walls occurs. Pocketsof high density drilling mud are retained within the wellbore as adetrimental residual characteristic of the cementing job. Therefore, inconventional procedures of cementing wellbores, having the presence ofhigh density drilling muds, there must be performed a continuousoperation of circulating cement therein the wellbore in order to insurethat a clean wellbore is associated with the cement introduced so that,subsequent to the washing operation, no pockets of high density drillingmud remain within the casing completion. Should high density drillingmuds remain and detrimental cementing of casing occur, inadequatecontacting of the casing cement with the wellbore results.

What is required is a method for removing high density drilling mudsfrom drilled wellbores so that the cementing of a casing string thereinmay be accomplished with adequate contacting of the casing, cement andwellbore walls being provided.

It is an object of the present invention to provide a method for thecementing of deep wells containing high density drilling muds.

It is a further object of the present invention to provide a method forsequentially introducing drilling muds into deep wells forthe removal ofhigh density drilling muds utilized in the drilling of the well for thesubsequent cementing of casing in the well.

It is still a further object of the present invention to provide amethod for the sequential injection of everdecreasing weight drillingmuds into wells for the total displacement of high density drilling mudwherein the displacement drilling muds subsequently introduced thereinexhibit miscibility with the cement utilized for the subsequentcementing of a casing string in the wellbore.

With these and other objects in mind, the present invention may be morefully understood by referral to the accompanying FIGURE and followingdescription.

SUMMARY OF THE INVENTION The objects of the present invention may beaccomplished through the use of a method of removing high densitydrilling mud from a wellbore for the subsequent cementing of casing. Themethod comprises injecting an ever-decreasing weight drilling mud intothe wellweight drilling mud injected having a density substantially thatof the high density drilling mud contained within the wellbore and withthe last portion thereof having a density similar to that of the cementto be utilized. In the method, the density of the ever-decreasing weightdrilling mud is varied by altering the particulate content of theever-decreasing weight drilling mud introduced into the wellbore.Generally, the high density drilling 'mud and the ever-decreasing weightdrilling mud have the same drilling mud base. A preferred drilling mudbase is water. However, should the drilling mud base be oil, afurtherstep in the method of the present invention comprises flushing the lastportion of the oil base ever-decreasing weight drilling mud from thewellbore through the introduction of a water base drilling mud havingsubstantially the same density as g the cement to be utilized.

Within the method of the present invention, the particulate materialutilized may have a density less than that of the drilling mud basewherein the method comprises. recirculating the produced drilling mudinto the wellbore together with additional particulate material added tothe produced drilling mud to decrease the density thereof. It is also anembodiment of the present invention that should the particulate materialutilized have a density greater than that of the drilling mud base. Inthis case the produced drilling mud is recirculated into the wellboretogether with additional drilling mud base added to the produceddrilling mud to decrease the density.

BRIEF DESCRIPTION OF THE DRAWING DETAILED DESCRIPTION OF THE INVENTIONThe present invention utilizes a sequential injection of anever-decreasing weight drilling mud into wells for the totaldisplacement of a high density drilling mud from the wellbore.Therefore, by continually decreasing the weight of the drilling mudintroduced, an even displacement of high density drilling mud from thewell is accomplished so that a drilling mud, having substantially thesame density as the cement to be utilized for the cementing of a casingstring to the well-bore wall, is present in the wellbore for thecementing operation. Through use of the method of the present invention,cement is easily introduced into the wellbore and evenly displaces thedrilling mud present in the well so that adequate contacting of thecasing, cement and the wellbore wall is achieved. By the present method,no residual high density drilling mud. is retained within the cementingoperation, thereby precluding the necessity of a continued recirculationof a low density drilling mud within the wellbore to remove the highdensity drilling mud previously contained therein.

Generally, for the cementing of the casing to the wellbore and thedisplacement ofa high density drilling mud contained within a well, thedisplacement mud should be of approximately the same consistency andhave the same base as that of the high density drilling mud utilized inthe drilling operation. Therefore, in the use of a water base drillingmud, having a high particulate content for high density achievement, thedisplacement drilling mud should also be a water base drilling mudhaving an ever-decreasing density, so that a uniform displacement of thehigh density drilling mud from the wellbore is achieved. It is preferredthat when the cement is introduced into the well, it contact a waterbase drilling fluid. Therefore, should an oil base drilling fluid beutilized in the drilling operation, an ever-decreasing concentration ofoil base mud, having a sequentially lowered density, should be utilizedfirst to clear the high density oil base mud from the well. Thesequential introduction is followed by circulation of a water basedrilling mud having the same or substantially the same density as thewater base cement to be utilized. Therefore, no water-oil interface isformed through the introduction of a water base cement and adequatecement completions may be accomplished.

Within the utilization of the present invention, the density of theever-decreasing weight drilling mud may be varied by altering theparticulate content of the ever-decreasing weight drilling mudintroduced into the wellbore. This particulate content may bemanipulated, for example by the use of a particulate material having adensity less than that of the drilling mud base through the introductionof further particulate material into the drilling mud as it isintroduced into the wellbore, or, in the case of particulate materialhaving a density greater than that of the drilling mud base, by thefurther introduction of drilling mud base into the drilling mud as it isintroduced into the formation. Should a particularly high densityparticulate material be utilized for the attainment of a high densitydrilling mud having coarse particulate matter contained therein, it maybe necessary to add particulate material having a lower density than theparticulate material utilized within the original high density drillingmud to obtain the ever-decreasing density drilling mud for displacementpurposes since an over-introduction of drilling mud base may hamper thewellbore completion by washing the wellbore and forming large cavitiestherein which are particularly difficult for easing completion purposes.Therefore, it is within the comprehension of the present invention thatmultiple forms of particulate material may be introduced within thedrilling mud to obtain the ever-decreasing drilling mud materialsdisclosed in the method.

The principles of the present invention may be more fully understood byreferral to the accompanying Figure. In the Figure, a wellbore 12 iscompleted from the earth s surface 1 1 through overburden rock 25, intoa subterranean reservoir 24. The wellbore has a casing string 14contained therein which is to be cemented to the wellbore 12. For thecompletion of the casing string 14, it is first necessary to remove ahigh density drilling mud 13 contained in the wellbore. Apparatusutilized to conduct the method of the present invention comprises anannulus outlet 15 connected to the wellbore at the surface and fed adrilling mud 17 through a valve assembly 16. This apparatus is utilizedto continually reduce the density of the drilling mud and mud weight byuse of a mud pump 18 connected to an inlet 19 directly aligned with thecasing string 14.

In the operation of the method of the present invention, the highdensity drilling mud 13 is displaced from the wellbore 12 through theannulus formed between the casing string 14 and wellbore 12 byintroduction of an ever-decreasing weight drilling mud within the easingstring 14. The ever-decreasing weight drilling mud is represented in theFigure by drilling mud slug 23 having a density slightly lower than thatof the high density drilling mud 13 and is followed by ever-decreasingweight drilling mud slugs 22, 21 and 20. The sequentially decreasingdensities of the drilling mud eventually reach a density similar to thatof the cement to be utilized in the completion of the casing string 14within the wellbore 12 so that the cement may easily be introducedwithin the system. This introduction allows the displacement of adrilling mud having essentially the same density and base as the cement,for example water, for its removal from the wellbore and for thecementing of the casing string 14 to the wellbore 12. As mentioned, whenthe drilling mud base is oil, the method further comprises flushing thelast portion of the oil base ever-decreasing weight drilling mud fromthe wellbore through the introduction of a water base drilling mudhaving substantially the same density as the cement to be utilized withsubsequent introduction of the cement into the wellbore for thecompletion of the casing string.

Although the introduction of ever-decreasing weight drilling mud in theaccompanying Figure is depicted as slugs being introduced within thewell, it is readily understood that the slugs are depicted only for thepurposes of illustration. The sequential introduction of a drilling mudinto the wellbore would normally be a continual decreasing of thedensity of the mud during the flushing operation. Although the slugmethod may be utilized when apparatus necessary for appropriate mixingand recirculation of drilling mud is not available, conventionaloperations are provided with a complement of mud pits and mud pumps, sothat the recirculation operation may be easily accomplished for thedisplacement of the high density drilling muds therefrom the wellbore.

The present invention then provides a method to circumvent theconventional procedures utilized for the cementing of wellboresexhibiting the presence of a high density drilling mud and eliminatesthe tedious operation of circulating cement therein the wellbore toinsure clean wellbores are associated with the cement. The methodinsures that pockets of high density drilling mud do not remain withinthe casing completion so that detrimental cementing of casing does notoccur and adequate contacting of the casing, cement and wellbore isachieved. Therefore, through utilization of the present method forremoving high density drilling muds from drilled wellbores, thecementing of casing strings therein may be accomplished with an adequatecontacting of the casing, cement and wellbore walls being providedthrough a simplified method utilizing conventional drilling mud andcementing apparatus.

The invention has been described herein with respect to particularembodiments and aspects thereof. It will be appreciated, however, bythose skilled in the art that various changes and modifications may bemade without departing from the scope of the invention as set forthherein.

Therefore, I claim:

LA method of removing a high density drilling mud from a wellbore forthe subsequent cementing of casing, which comprises injecting anever-decreasing weight drilling mud into the wellbore with the firstportion of the ever-decreasing weight drilling mud having a densitysubstantially that of the high density drilling mud contained within thewellbore and with the last portion thereof having a density similar tothat of the cement to be utilized for the casing completion.

2. The method of claim 1 wherein the density of the ever-decreasingweight drilling mud is varied by altering the particulate content of theever-decreasing weight drilling mud introduced into the wellbore.

3. The method of claim 2 wherein the high density drilling mud and theever-decreasing weight drilling mud have the same drilling mud base.

4. The method of claim 3 wherein the drilling mud base is water.

5. The method of claim 3 wherein the drilling mud base is oil, andfurther comprising flushing the last portion of the oil baseever-decreasing weight drilling mud from the wellbore through theintroduction of a water base drilling mud having substantially the samedensity as the cement to be utilized.

6. The method of claim 2 wherein the particulate material utilized has adensity less than that of the drilling mud base and further comprisingrecirculating the produced drilling mud into the wellbore along withadded particulate material.

7. The method of claim 2 wherein the particulate material utilized has adensity greater than that of the drilling mud base and furthercomprising recirculating the produced drilling mud into the wellbore byadding drilling mud base thereto the produced drilling mud.

1. A method of removing a high density drilling mud from a wellbore forthe subsequent cementing of casing, which comprises injecting anever-decreasing weight drilling mud into the wellbore with the firstportion of the ever-decreasing weight drilling mud having a densitysubstantially that of the high density drilling mud contained within thewellbore and with the last portion thereof having a density similar tothat of the cement to be utilized for the casing completion.
 1. A methodof removing a high density drilling mud from a wellbore for thesubsequent cementing of casing, which comprises injecting anever-decreasing weight drilling mud into the wellbore with the firstportion of the ever-decreasing weight drilling mud having a densitysubstantially that of the high density drilling mud contained within thewellbore and with the last portion thereof having a density similar tothat of the cement to be utilized for the casing completion.
 2. Themethod of claim 1 wherein the density of the ever-decreasing weightdrilling mud is varied by altering the particulate content of theever-decreasing weight drilling mud introduced into the wellbore.
 3. Themethod of claim 2 wherein the high density drilling mud and theever-decreasing weight drilling mud have the same drilling mud base. 4.The method of claim 3 wherein the drilling mud base is water.
 5. Themethod of claim 3 wherein the drilling mud base is oil, and furthercomprising flushing the last portion of the oil base ever-decreasingweight drilling mud from the wellbore through the introduction of awater base drilling mud having substantially the same density as thecement to be utilized.
 6. The method of claim 2 wherein the particulatematerial utilized has a density less than that of the drilling mud baseand further comprising recirculating the produced drilling mud into thewellbore along with added particulate material.